In recent years, the range of applications for magnetic recording apparatus such as magnetic disk devices, floppy (a registered trademark) disk devices and magnetic tape devices has expanded enormously, and not only has the importance of such devices increased, but the recording density of the magnetic recording media used in these devices has also continued to increase markedly.
Since the introduction of MR heads (Magnetoresistive heads) and PRML (Partial Response Maximum Likelihood) techniques, the increase in surface recording densities has become even more dramatic, and the more recent introduction of GMR heads (Giant Magnetoresistive heads) and TMR heads (Tunnel Magnetoresistive heads) and the like has meant that recording densities continue to increase at a pace of approximately 100% per year.
There are still strong demands for even higher recording densities for these magnetic recording media, and in order to satisfy these demands, higher coercive force and higher signal to noise ratio (SN ratio) of the magnetic recording layer and higher levels of resolution are requested. Further, in recent years, the absolute film thickness of the medium has been reduced in order to attain higher surface recording density, but this has lead to a problem wherein this reduced thickness is accompanied by a phenomenon in which the recording magnetization is weakened by thermal disturbances, and the thermal stability of the recording is becoming a significant technical issue. In particular, attempts to improve the aforementioned SN ratio have frequently resulted in a deterioration in the thermal stability, and combining a high SN ratio with superior thermal stability has become a particular target of current research and development. Generally, in a medium having an excellent SN ratio, the crystal grain size of the magnetic grains that constitute the magnetic layer is usually very small, and although this small grain size is effective in terms of suppressing medium noise, it means that the thermal stability of the magnetization is close to the unstable region.
Furthermore, in recent years, concurrently with the improvements in linear recording density, efforts are also continuing into raising the surface recording density by increasing the track density, and in the most recent magnetic recording apparatus, the track density has reached 110 kTPI. However, as the track density is increased, mutual interference tends to occur between the magnetically recorded information within adjacent tracks, and the resulting magnetized transition region in the boundary region between the tracks acts as a noise source, easily causing problems such as a deterioration in the SN ratio. This leads directly to a reduction in the bit error rate, and is therefore an impediment to achieving increased recording densities.
Further, because the distance between tracks narrows, the magnetic recording apparatus requires extremely high-precision track servo technology, and a method is usually employed where recording is executed over a comparatively wide range, and reproduction is then executed across a narrower range that that used during recording in order to exclude, as far as possible, effects from adjacent tracks. Although this method enables inter-track effects to be suppressed to a minimum, achieving a satisfactory reproduction output level can be difficult, and therefore ensuring an adequate SN ratio is also difficult. In recent years, perpendicular magnetic recording media have been used to ensure satisfactory thermal stability for the above types of media.
In this manner, perpendicular magnetic recording media are used as a technology to achieve higher recording density, but in order to achieve even further high recording density in perpendicular magnetic recording, the track density must be increased. Furthermore, “fringing” of the recording edge portions, which tends to become problematic in perpendicular magnetic recording media as the track density is increased, must be reduced.
One example of a method of avoiding this fringing is a discrete track medium (for example, see Patent Documents 1 and 2 listed below).
Patent Document 1 proposes a structure for a discrete medium in which the data regions are formed as convex portions and guard bands are formed as concave portions. However, providing these concave-type guard bands results in the formation of concave-convex portions on the disk surface, which tends to have an undesirable effect on the floating properties of the magnetic recording head and therefore it is not preferable.
Patent Document 2 proposes a discrete medium with a flat disk surface in which guard bands are filled with an embedding material. Examples for this guard band member include oxides, nitrides, carbides, borides, and polymer compounds.
An example of the method used for embedding an oxide or the like in the guard bands of a discrete medium is a method in which a sputtering method or the like is used to deposit a film of an oxide or the like on both the guard bands and the data regions of the discrete medium, and the surface of that film is then etched by ion beam etching or the like to re-expose the data regions of the discrete medium, thereby forming data regions that are patterned by the guard bands on the surface of the discrete medium. A protective film is then formed on top of the object to complete formation of the discrete medium.
Furthermore, Patent Document 3 discloses the use of a photocurable resin having fluidity during the formation of the guard bands (non-magnetic regions) of a discrete medium.
Patent Document 4 discloses the use of a siloxane-based polymer compound with a weight average molecular weight of not less than 1,000 and not more than 50,000 which has the function of causing a photocuring reaction for nanoimprinting. Further, Patent Document 5 discloses a method of forming a very fine SiO2 pattern on a substrate surface by applying a mixture of a hydrogenated silsesquioxane polymer and a solvent to the substrate surface, embossing a very fine pattern into the coated surface, and then removing the solvent and performing hydrolysis curing.
[Patent Document 1]    Japanese Unexamined Patent Application, First Publication No. Hei 6-259709
[Patent Document 2]    Japanese Unexamined Patent Application, First Publication No. Hei 9-97419
[Patent Document 3]    Japanese Unexamined Patent Application, First Publication No. 2005-100496
[Patent Document 4]    Japanese Unexamined Patent Application, First Publication No. 2007-072374
[Patent Document 5]    Japanese Unexamined Patent Application, First Publication No. 2003-100609